I just received my new GPSMAP 64st. I've been trying to install unlocked maps from this forum (eg [Only registered and activated users can see links. ]) by downloading the unlocked .img file and transfer it by USB to /GARMIN/gmapsupp.img. However, this fails every time and I keep getting "cannot authenticate maps" displayed when rebooting the device. I've also tried other maps, with the same issue.
Does anyone have any idea how to solve this?